1. Field of the Invention
This invention relates generally to a tablet with a short testing function and method of forming it. More particularly, the invention relates to the tablet and method that could measure the short between different conductive lines which forms an antenna array.
2. Description of the Prior Art
The current handwriting recognition system at least has the tablet and the wireless pen. The user moves the wireless pen over the tablet for inputting a message, just as the user uses a conventional paper and pen, and the tablet receives the message transmitted from the wireless pen to decide both the location of the wireless pen and the current working mode.
FIG. 1A and FIG. 1B show the basic structure of conventional tablet, at least has following elements in and on base 11: processing device 12, numerous conductive lines 13 and ground point 14. Moreover, each conductive line 13 has a first terminal which is electrically coupled with ground point 14 and a second terminal which is electrically coupled with processing device 12, the layout of all elements is that all conductive lines 13 forms an antenna array but are separate from each other, and processing device usually is located on the edge of base 11. Herein, ground point 14 is used to let all conductive lines 13 have same potential, to avoid processing device 12 producing errors during analysising messages from conductive lines 12. Certainly, because conductive lines 13, or antenna array, must be able to distinguish the location of the wireless pen, conductive lines 13 can not only distributed along the X-axis or the Y-axis of the plane coordinate. Further, base 11 usually are multi-layer board to provide conductive line 13 enough space for distributing, and the layout of conductive lines 13, or the layout of antenna array, also has numerous variations. Herein, FIG. 1A and FIG. 1B only show a possible layout: upper layer and lower layer are used to measure X-axis messages and Y-axis messages separately, but two layers use same processing device 12 and same ground point.
Obviously, when a short occurs between different conductive lines 13, the real transmitted paths of electrical messages among these conductive lines are different from the predetermined transmitted paths of electrical messages among these conductive lines. Thus, messages along any specific conductive line 13 would be interfered by message along other conductive lines 13 while the specific conductive line 13 is shorted, and then processing device 12 would not be able to decide the location of the wireless pen by analyzing messages from different conductive lines 13.
Furthermore, because all conductive lines 13 are electrically coupled with ground point 14, it is impossible to decide whether the short has happened and where the short has happened only by measuring the resistance between different conductive lines 12. Conventional fabrications almost check quality of tablet by human efforts, and then unavoidable defects are low efficiency and high failure, especially while base 11 is made of multi-layer board and pattern density within tablet being increased.
In short, current technologies are not able to decide whether a short has happened and where the short has happened, and then it is desired to develop a new technology to check short within tablet.
One main object of the invention is to effectively check whether tablet has unexpected short.
Another object of the invention is to decide whether the table has a short and where the short is with minimizing modification of both structure and fabrication of tablet.
Because conventional technology electrically couples all conductive lines with ground point, the short could not be found only by simply measuring the resistance between different conductive lines. The invention propose a key of solution: the object of electrically coupling conductive lines with the ground point is to ensure messages transmitted on different conductive lines have same referring level. In other words, it is not desired to electrically couple all conductive lines with the ground point before the tablet is operated, such as during the period of checking an abnormal short within the tablet.
Therefore, the invention solves conventional problems by inserting a switch in one terminal of conductive line which is closed to ground point. Initially, all switches are turned off to let all conductive lines, at least almost all conductive lines, become electrically separated from the ground point. Thus, each conductive line should be separated from other conductive lines, and then it is possible to detect a short by simply measuring the resistance between different conductive lines. Further, after the detection of a short is finished, all switches are turned on to let all conductive lines be electrically coupled with the ground point, and then the tablet could be used to receive messages from the wireless pen.